The instant invention relates to silsesquioxane-titania hybrid polymers useful to form anti-reflective coatings in the microelectronics fabrication industry.
The microelectronics fabrication industry is moving toward smaller geometries in its devices to enable lower power and faster speeds. As the conductor lines become finer and more closely packed, more challenges are introduced into manufacturing of semiconductor devices. One of the most important of these manufacturing processes is photolithography.
Linewidth variations in patterns produced by photolithography can result from optical interference from light reflecting off an underlying layer in a semiconductor device. Variations in photoresist thickness due to topography of the underlying layers can also induce linewidth variations. Bottom anti-reflective coatings (BARC) applied under a photoresist layer have been used to prevent interference from reflection of the irradiating beam. In addition, if a planarizing anti-reflective coating is selected, surface topography can be reduced by the application of the BARC film, thereby, improving photoresist uniformity which also results in improved (reduced) linewidth variation.
For some lithographic processes, especially at finer integration nodes where line widths become even smaller, photoresists are no longer able to provide sufficient etch resistance to enable effective pattern transfer to the layer underneath the resist. In many instances (e.g., where a very thin photoresist layer is required, where the underlayer material is very thick, where deep etching is required, or where the composition of the photoresist and BARC and/or underlayer material are very similar in chemical nature), a hardmask layer may be employed as an intermediate layer between the resist, BARC (if used) and underlying layer (i.e. dielectric layer, silicon, polysilicon, etc.) to be patterned. The hardmask layer receives the pattern from the patterned resist and is able to withstand the etching processes needed to transfer the pattern to the underlayer. In the most desirable case, the hardmask layer and BARC layer can be combined as one to simplify the integration process and lower manufacturing costs.
Dual damascene integration schemes are now also being used to reduce manufacturing costs in the back end of the line (BEOL) of fabrication. The lithographic processes required for dual damascene integration add another degree of complexity to photolithography. Unlike conventional (single damascene) processes, which require only patterning of vias, the process for making dual damascene structures also requires patterning of line/space combinations for trenches that will be etched into relatively thick transparent layers of dielectrics. In order to ensure that barrier layers used, for example, to prevent copper (or alternate metal) oxidation or act as an etch stop, are not etched clear during the dielectric etch, sufficient selectivity between the barrier layer (i.e. silicon nitride) and dielectric material (i.e. silicon dioxide) is required. Unfortunately, the etch selectivity requirements often result in poor etch profiles and/or polymer build-up in the vias and trenches.
One method of mitigating this problem is to fill the etched via with an etch-resistant material prior to trench patterning and etch. This prevents the barrier layer material from being exposed to etch gases during the dielectric trench etch. Organic gap-fill materials, such as photoresists or organic BARCs, can be used in this application. However, when inorganic dielectric materials are used etch defects can result due to the differences in etch rates between the organic fill material and the inorganic dielectric. Elimination of these defects without damaging barrier layers can be difficult.
Many hardmask, anti-reflective coatings and gap-fill materials have been described in the literature and prior art, however, none of these materials provide a perfect solution to the problems faced during state-of-the-art lithography processes. In the worst of cases, single solution materials are used, resulting in increased manufacturing complexity and costs. Many of the prior art materials that provide dual- or multi-functionality are difficult to apply to substrates, e.g., they must be applied using chemical or physical vapor deposition and/or require high temperature baking after deposition which is incompatible with photoresist processing. Many of these materials also either do not provide reflection control or only control reflection through destructive interference of the reflected light. This results in stringent thickness and uniformity controls on the films. It is, therefore, desirable from a manufacturability standpoint to have anti-reflective coatings/hardmask compositions which provide both masking and true anti-reflective properties (i.e. through absorption and interference rather than solely by interference). It is further desired that these coatings be applied using spin-coating and thermal treatment techniques that are compatible with typical photoresist processes. Furthermore, the material should have sufficient etch selectivity with regard to the overlying photoresist. In the case of dual damascene integration schemes, the coating should also be able to fill vias and have similar etch characteristics to the trench dielectric material while being selective to any metal barrier layers.
Anti-reflective coatings can be used on top of (TARC) or directly underneath (BARC) a layer of photoresist to minimize the amount of non-imaging light that is reflected during the photolithography process by absorption and/or destructive interference. The minimization of non-imaging light reflections can result in an improvement (minimization) in line-width variations and reduced line edge roughness (LER) of the imaged photoresist, thereby, improving critical dimension (CD) control.
Anti-reflective coating layers and techniques for their incorporation in electronic devices are disclosed in the following references: “Materials evaluation of anti-reflective coatings for single layer 193 nm lithography”, Kunz, R. R., et al, SPIE, (1994) 2195, 447-460; “Anti-reflective Coatings, a Story of Interfaces”, Semiconductor International, (1999), 55-60; Lin, et al., “Dual layer Inorganic SiON Bottom ARC for 0.25 um DUV Hard Mask Applications, SPIE, (2000), 246; “Anti-reflective Coatings; Theory and Practice”, SPIE, (2004), 118.
Silsesquioxane resins are well known in the microelectronics art; see, for example, U.S. Pat. Nos. 6,891,237, 3,615,272 and 5,973,095. The polymer films produced from these resins, however, generally do not exhibit the anti-reflective properties required for BARC applications at, for instance, 248 nm and 193 nm imaging wavelengths. In order to provide BARC functionality, a chromophore species, often referred to as a dye, must be added to the system. The dye is chosen to give the proper absorption over the imaging wavelengths used during photolithography. In general, these dye phases are not incorporated directly into the polymer backbone. Rather they are added as an additive to the final BARC formulation and are not bound to a side chain in the polymer structure and/or are not covalently bonded to the polymer network. Examples of such dyed hybrid BARC systems have been described in U.S. Pat. No. 6,420,088, and US Publication No. 2002/0128388.
Adequate absorption at 248 nm may be obtained by incorporating species such as anthracene or naphthalene into the polymer matrix, as described, for example in U.S. Pat. No. 6,268,457. While these species will add the desired level of 248 nm absorption to help control reflectivity, they can reduce the inorganic content of the final films. This may negatively impact hardmask properties such as etch selectivity. In addition, these species are often only weakly bound into the polymer network, resulting in difficulties controlling the stability of films produced from such systems. Stability issues manifest themselves in property drift, such as etch rates and extinction coefficients, as a function of film age, especially when films are exposed to ambient light and environments.
Synthesis of silsesquioxane-titania hybrid polymers useful to form anti-reflective coatings in the microelectronics fabrication industry is known; see, for example, Chen et al., Materials Chemistry and Physics, 83 (2004) 71-77 herein fully incorporated by reference. Such formulations are advantaged over those which utilize organic chromophores in that the inorganic content is not compromised by the addition of the chromophore species. However, the titania domain size of the prior art silsesquioxane-titania hybrid polymers is relatively large and limits the usefulness of such polymers to form anti-reflective coatings in advanced integration nodes (feature sizes below 180 nm) in the microelectronics fabrication industry. Other silsequioxane-titania hybrid polymer systems are described in U.S. Pat. No. 5,100,503, but the titania species in these polymers are not bound into the polymer network, allowing the chromophore phase to be readily filtered out during standard processing, thereby, greatly reducing, or even eliminating the desired 248 nm adsorbing species.